1. Field of the Invention
The present invention generally relates to an in-cell touch screen, and more particularly to a controller adapted to a self-capacitance in-cell touch screen.
2. Description of Related Art
A touch screen is an input/output device that combines touch technology and display technology to enable users to directly interact with what is displayed. A capacitor-based touch panel is a commonly used touch panel that utilizes capacitive coupling effect to detect touch position. Specifically, capacitance corresponding to the touch position changes and is thus detected, when a finger touches a surface of the touch panel.
In order to produce thinner touch screens, in-cell technology has been adopted that eliminates one or more layers by building capacitors inside the display. In conventional in-cell touch screens, a common voltage (VCOM) layer is used in a display mode and a touch sensing mode. The common voltage in the display mode usually has a negative voltage level, while a sensing signal induced on receiving (RX) electrodes of the VCOM layer in the touch sensing mode usually has a positive voltage level, resulting in a spanning voltage exceeding the operating voltage of metal-oxide-semiconductor (MOS) transistors implementing switches that alternate the display mode and the touch sensing mode. Accordingly, an additional circuit is thus required to supplement the switches to solve the spanning (positive to negative) voltage problem. Alternatively, MOS transistors with high operating voltage are used instead to implement the switches in order to solve the spanning voltage problem. Unfortunately, either scheme causes increase in circuit area. Therefore, a need has arisen to propose a novel scheme for reduction of circuit area for in-cell touch screens.